Polyphenols in lahpet-so and two new catechin metabolites produced by anaerobic microbial fermentation of green tea

The phenolic constituents of lahpet-so, a traditional postfermented tea of Myanmar produced under anaerobic conditions, were examined. The major polyphenols were identified to be pyrogallol and 4′-hydroxyphenyl-3-(2′′,4′′,6′′-trihydroxyphenyl)-propan-2-ol, 3′,4′-dihydroxyphenyl-3-(2′′,4′′,6′′-trihydroxyphenyl)-propan-2-ol, and 3′,4′,5′-trihydroxyphenyl-3-(2′′,4′′,6′′-trihydroxyphenyl)-propan-2-ol. The hydroxydiphenylpropan-2-ols were identical to the initial metabolites produced from green tea catechins by mammalian intestinal bacteria. In addition, an anaerobic mixed-fermentation experiment using lahpet-so and Japanese commercial green tea afforded two new catechin degradation products together with known compound bruguierol B and the above-mentioned catechin metabolites. Based on spectroscopic evidence, the structures of the new compounds were concluded to be 4-(2,5-dihydroxyhexyl)benzene-1,2-diol and (5S,8R)-6,7,8,9-tetrahydro-5-methyl-5·8-epoxy-5H-benzocycloheptene-2,3,4-triol. Interestingly, the production mechanism was deduced to be the inverse of the biosynthesis of the flavan-3-ol A ring.